Interferon-α Therapy for Hairy Cell Leukemia and Lymphoproliferative Disorders Simulating Hairy Cell Leukemia (Hairy Cell Leukemia Variant): A Cooperative Group Study in Japan

Abstract

Interferon-α (IFN-α) is highly effective in the treatment of hairy cell leukemia (HCL) in western countries. The efficacy of IFN-α in Japanese patients with HCL has not been determined, who have considerably different hematologic features from those of HCL patients in western countries. In the present study, the clinical effects of human lymphoblastoid interferon in 17 patients with HCL and 5 patients with lymphoproliferative disorders simulating HCL (tentatively designated as hairy cell leukemia variant) in Japan were tested.
Fifteen of 17 HCL patients completed at least eight weeks of treatment and were evaluated: IFN-α was discontinued in two patients because of severe leukopenia and skin eruption, respectively. There were one complete and five incomplete remission, and overall response rate was 40%, which was significantly lower than those reported in western countries. The clinical, hematologic findings of 15 patients were compared to those of HCL patients in western countries. Only one patients, who achieved complete remission, had hematologic and immunophenotypic features entirely compatible with those of typical HCL in western countries. In contrast, the remaining 14 patients differed considerably from the formers and were classified in Japanese type HCL, a type of HCL found in most HCL patients in Japan. Two additional HCL patients showed more than 50% reduction in bone marrow hairy cell and some improvement of cytopenias, while none of five patients with hairy cell leukemia variant responded to IFN-α.
These findings suggest that the difference in the efficacy of IFN-α between HCL in Japan and in western countries may be due to the difference in the type of HCL, although the relatively low sensitivity of Japanese type HCL to IFN-α remains unexplained.